The invention relates to a closed level control system for a vehicle having pressurized medium chambers via which a vehicle body is suspended relative to at least one vehicle axle. The closed level control system includes: a supply vessel containing a pressurized medium; at least one pressurized medium chamber, which is operatively connected to the pressurized medium supply vessel in such a manner that the pressurized medium can be transferred from the pressurized medium supply vessel into the pressurized medium chamber or pressurized medium from the pressurized medium chamber can be transferred into the pressurized medium supply vessel; and, a pump with which a pressurized medium can be transferred from the pressurized medium chamber into the pressurized medium supply vessel or vice versa.
A level control system of this kind incorporating an air spring arrangement is disclosed in German patent publication 3,339,080. The air spring arrangement described in this publication affords the advantage that only one pressurized air supply vessel is required into which air is pumped from the air springs with the aid of a pump or air is pumped from the pressurized air supply vessel into the air springs. The air spring arrangement is, however, so built up that the pump must pump in two directions and this causes the pump to have a complex configuration.
It is an object of the invention to provide a closed level control system which has a simple configuration and can be driven by a pump which can pump the pressurized medium only in one direction.
The closed level control system of the invention is for a vehicle having a vehicle body, vehicle axles and pressurized medium chambers with which the vehicle body is suspended relative to corresponding ones of the vehicle axles. The closed level control system includes: a pressurized medium supply vessel for holding a medium under pressure as a pressurized medium; a pump for transferring the pressurized medium between the supply vessel and the pressurized medium chambers; the pump having an input and an output and the pump being configured so as to permit the pump to pump the pressurized medium from the input to the output thereof; a first controllable directional valve; a second controllable directional valve; a first pressurized medium line connected to the supply vessel and being connected via the first controllable directional valve to the input of the pump; a second pressurized medium line connected to the pressurized medium chambers and being connected via the second controllable directional valve to the output of the pump at least when the pressurized medium is to be transferred from the supply vessel into the pressurized medium chambers; a third pressurized medium line connected to the pressurized medium chambers and being connected via the first controllable directional valve to the input of the pump; and, a fourth pressurized medium line connected to the supply vessel and being connected via the second controllable directional valve to the output of the pump at least when pressurized medium is to be transferred by the pump from the pressurized medium chambers into the supply vessel.
The basic idea of the invention is that when a pressurized medium is to be pumped from the pressurized medium supply vessel into a pressurized medium chamber, then the input of the pump is connected to the pressurized medium supply vessel and the output of the pump is connected to the pressurized medium chamber. If, in contrast, pressurized air is to be pumped from a pressurized medium chamber into the pressurized medium supply vessel, then the input of the pump is connected to the pressurized medium chamber and the output of the pump is connected to the pressurized medium supply vessel.
The advantage achieved with the invention is especially seen in that the air is always pumped from the input to the output of the pump independently of whether the air is pumped from the pressurized medium supply vessel into a pressurized medium chamber or in the opposite direction. In this way, the pump only has to pump in one direction and therefore can be configured in a simple manner. A further advantage of the invention is that only few directional valves, which incur cost, are needed in the level control system.
According to another feature of the invention, the level control system includes two controllable directional valves via which the pressurized medium lines are connected. One of the controllable directional valves is arranged at the input and the other controllable valve is arranged at the output of the pump. The advantage of this embodiment is that the number of controllable directional valves, and therefore the cost thereof, is held as low as possible.
According to another feature of the invention, the level control system includes two controllable directional valves and a changeover valve. The pressurized medium lines are connected to the input of the pump from time to time and are conducted via at least one of the first and second controllable directional valves to the input of the pump and the pressurized medium lines, which are from time to time connected to the output of the pump, are conducted to different inputs of the changeover valve which is located at the output of the pump.
According to another feature of the invention, the pressurized medium line, which extends from the pressurized medium supply vessel and can be connected to the input of the pump, is connected directly to the pressurized medium line, which extends from the pressurized medium chamber and can be connected to the input of the pump, when both controllable directional valves are simultaneously in the switched state. The advantage of this embodiment is that the air can be conducted directly (that is, without that the air is conducted through the pump) from the pressurized medium supply vessel into the pressurized medium chamber when the pressure of the pressurized medium in the pressurized medium supply vessel is greater than in the pressure chamber. The same applies for the opposite direction.
According to still another embodiment of the invention, the input of the pump is connected via a controllable valve to an external pressurized medium reservoir (that is, not to a reservoir belonging to the level control system) and a pressurized medium line, which extends from the pressurized medium supply vessel, is connected to the output of the pump when the pressurized medium supply vessel is filled up from the external pressurized medium reservoir by means of the pump. The advantage of this embodiment is that the losses of pressurized medium in the pressurized medium supply vessel (for example, because of leakage) can be compensated in that pressurized medium from the pressurized medium reservoir is pumped into the pressurized medium supply vessel with the aid of the pump. Here too, the pump pumps from the input to the output.
According to another feature of the invention, the level control system includes a pressure sensor which is mounted in one of the pressurized medium lines leading away from the pressurized medium chamber. A controllable directional valve is located between the pressurized medium chamber and the pressure sensor and, in a first switching state, the directional valve separates the pressurized medium chamber from the pressure sensor and, in a second switching state, the directional valve connects the pressurized medium chamber to the pressure sensor. The advantage of this embodiment is that, with the aid of the pressure sensor, the pressure in the pressurized medium supply vessel as well as the pressure in the pressurized medium chambers can be measured. How this is done in detail will be explained in connection with the description of the drawings hereinafter. The measured pressure values can be applied to evaluate whether, when pumping the pressurized medium from the pressurized medium supply vessel into the pressurized chamber or vice versa, the pump needs to pump. This is necessary when there is no pressure drop in the desired flow direction of the pressurized medium.
According to still another embodiment of the invention, the controllable directional valves are configured as electrically controllable directional valves. The advantage of this embodiment is that electrical controllable directional valves are commercially available as cost-effective standard components.